A Concealed Left-Sided Accessory Pathway with Nodoventricular Conduction Features: A Case Report

Background Nodoventricular accessory pathways are rare connections between the atrioventricular node and ventricular myocardium, typically exhibiting decremental conduction and often mimicking atrioventricular nodal re-entrant tachycardia (AVNRT). Their diagnosis remains challenging, particularly in the absence of manifest pre-excitation. Case Summary A 30-year-old male with recurrent paroxysmal supraventricular tachycardia (SVT) underwent electrophysiological study. ECG showed no pre-excitation. Pacing maneuvers revealed concentric, decremental ventriculoatrial conduction, no evidence for dual atrioventricular conduction. Adenosine induced complete anterograde and retrograde block. The tachycardia is induced during programed atrial stimulation with eccentric coronary sinus activation. The tachycardia is terminated during ventricular overdrive pacing by a fusion beat as well as ventricular extrastimulation without atrial capture in a transition zone, which supported the diagnosis of a nodoventricular accessory pathway with left-sided extension participating in orthodromic AV re-entrant tachycardia. Successful ablation done on the left posterolateral aspect of the mitral annulus with no further tachycardia induction. Conclusion Nodoventricular accessory pathways remain an important but often concealed cause of SVT. This case highlights a rare presentation involving left-sided extension and demonstrates how detailed electrophysiological assessment can distinguish this entity from other tachycardias. Consideration of this mechanism is essential to ensure accurate diagnosis and safe therapeutic decision-making.